Since all the seeds exposed to
mutagenic treatments do not have equal genetic damage, it could be of
great help if plants with more mutagenic damage are identified in the M-j
generation itself. This would facilitate recovery of a high frequency of
mutations in the succeeding generations.

The phenomenon of leaf aberrations
(a-sectors, 2) due to mutagenic treatment was first reported in peas as
early as 1925 (1 ) and it was demonstrated subsequently in a wide variety
of crop plants. It was also established by several studies that the degree
of leaf aberrations in M1 is strongly correlated with the frequency of
macromutations in M2 generation. M1 sterility has also been used as an
index of mutagenic damage. Although a positive correlation between leaf
aberrations, M1 sterility and M2

macromutation frequency is well
established, such a relationship has not been demonstrated for the more
complex micromutations.

In the experiment reported here leaf
aberrations and sterility were used as screening criteria. Seeds of pea
variety DMR-3 were treated with gamma-rays, ethylene imine (EI) and N-nitroso ethyl urea
(NEU). The entire M1 population was divided into four groups on the basis
of leaf aberrations at seedling
stage and again on the basis of
sterility at the adult plant stage: low degree of leaf aberrations + low
sterility (LL), high degree of leaf aberrations + low sterility (HL), low
degree of leaf aberrations + high sterility (LH), and high degree of leaf
aberrations + high sterility (HH). Single plant progenies were grownin separate rows in the M2 generation, and observations were recorded
forboth macromutations (chlorophyll + morphological) and
micromutations (five polygenic traits, namely, days to flowering,
pods/plant, seeds/pod, 100-seed weight and yield/plant). The promising
mutagenized progenies were identified on the basis of higher mean and CV
(variability) than the progeny having the highest mean and CV in the control
(untreated) population. In the M3 generation, the character mean was used
as the criterion for selection of promising progenies, since intra-family
variance is expected to be reduced in this generation.

Table 1 shows that the CV values in
M2 were highest in the HH group and lowest in the LL group of mutagenic
damage. The HL and LH groups were intermediate. This trend was constant
for all the five polygenic characters studied and was also confirmed in the M3 generation
where only the HH and LL groups were studied more intensively. The
comparison of CV values between HL and LH groups in M2 revealed a very
interesting picture: the CV values in HL group were higher than in LH
group for all the five polygenic traits (Table 1). This suggests that leaf
aberrations are a better index of mutagenic damage than sterility.
Further, since the CV in the LH group was also significantly higher than
in the LL group, the sterility parameter serves as a reliable additional
criterion for classifying the mutagenized material further on the basis of
genetic damage.

The analysis of macromutations in
the M2 generation also revealed a similar pattern as for micromutations
(Fig. 1). The groups of mutagenic damage were arranged in the following
order on the basis of frequency of macromutations: HH > HL > LH >
LL.

58PNL Volume 211989RESEARCH
REPORTS

Thus the grouping of M1 plants on
the basis of M1 damage (leaf aberrations and sterility) can be of great
help in identifying plants with maximum mutagenic damage which are likely
to yield a higher frequency of mutations in the M2 and M3
generations.This
helps to reduce the volume

of unwanted (nonmutated or poorly
mutated) material, thereby saving time and labor in the isolation of
mutations.

1. Arntzen, L. and C. Krebs. 1925. Acta Radiol. 4:
5-31.

2. Blixt, S. 1965. Agri Hort.
Genet. 23:172-186.

TabLe 1. Effect of grouping on the
basis of mutagenic damage in M-| on the magnitude of induced variability
(CV%) and means for various characters in M2 and M3
generations.

Character

M2 generation, groups

M3 generation, groups

LL

HL

LH

HH

LL

HH

CV

Mean

CV

Mean

CV

Mean

CV

Mean

CV

Mean

CV

Mean

Days to flowering

7.3

75.1

8.1

75.5

7.7

74.9

8.6

75.8

7.7

74.3

8.7

75.3

Pods/plant

29.1

17.0

34.2

18.0

31.3

17.2

37.7

18.8

34.7

7.1

39.
3

7. 7

Seeds/pod

22.0

.3.5

23.6

3.7

22.6

3.6

25.4

3.8

24.3

3.3

26.3

3.5

100-seed weight

14.3

16.8

16.4

16.9

15.6

16.8

17.5

17. 1

15.4

16.7

17.2

1 7.0

Seed yield/plant

36.7

7.3

38.9

7.6

37.1

7.1

40.9

8.4

38.0

3.9

41
.2

4.2

Note: The groups of mutagenic
damage (LL, HL, LH and HH) were assigned on the basis of low or high
degree of a-sectors and high or low degree of induced sterility in M1 .